Monsanto Co. and Alnylam Pharmaceuticals Inc. said Tuesday that they have formed a strategic alliance to advance biological technologies in the field of agriculture. Monsanto will pay $29.2 million in upfront payments to Alnylam, a Cambridge company that is seeking to develop drugs with its RNAi gene-silencing technology. To date, Alnylam has no products on the market. Under Tuesday’s agreement, Monsanto said it has received worldwide, exclusive rights to use Alnylam’s platform technology and intellectual property in the field of agriculture, including the ability to grant sublicenses.